1. Field of the Invention
The present invention relates to a semiconductor memory device in which an insulation film having a high dielectric constant is formed as an insulation film between electrodes.
2. Description of the Related Art
In a next-generation nonvolatile semiconductor memory device, a distance among cells is shrinked. Consequently, as regards an insulation film between electrodes that is formed between a charge storage layer and a control electrode, the inter-cell distance is made less than in the prior art. As a result, in a three-dimensional structure that is adopted in, e.g. an ONO film (three-layer film of silicon oxide film/silicon nitride film/silicon oxide film), interference between adjacent cells increases conspicuously. This leads to degradation in device characteristics, and it becomes difficult to achieve an increase in area using the three-dimensional structure.
In order to realize the next-generation semiconductor memory device, it is necessary to use, as the inter-electrode insulation film, an insulation film having a higher dielectric constant than in the prior art. The use of the high dielectric constant film can increase the capacity without increasing the area. This makes it unnecessary to use the three-dimensional structure, and the fabrication process is simplified. As a result, the device performance can be enhanced, the manufacturing method can be simplified, and the fabrication steps with a high yield can also be realized.
Jpn. Pat. Appln. KOKAI Publication No. 2001-223282 discloses a nonvolatile memory device using (TaO)1−x(TiO)xN(0.01≦x0.09) as a high dielectric constant film. This technique is directed to improve the problem of leak current and to enhance the mechanical and electrical strength of the film. Jpn. Pat. Appln. KOKAI Publication No. 2001-210734 discloses that a TaON film is used as an inter-electrode insulation film, thereby obtaining a high electrostatic capacitance.